X-ray fluorescence (XRF) is a well known technology for analysis of the elemental composition of solid materials. In XRF, a focused X-ray beam is directed onto the surface of a sample. Atoms in the sample responsively emit X-ray photons having characteristic energies. One or more X-ray detectors are used to collect and convert the X-rays emitted by the sample into electronic signals that may be processed to determine the energy and number emitted of X-rays, which in turn provides information regarding the abundance of elements in the sample. XRF analyzers are commercially available in both laboratory (stationary) and portable forms. Field portable XRF analyzers situate the X-ray source, detector and related electronics within a handheld housing, and may be easily transported between inspection stations in an industrial manufacturing or processing facility or to the field for in situ analysis.
Because the sensitivity of XRF decreases with decreasing proton number (Z), XRF devices are generally not capable of quantitative analysis of light elements in the sample. For example, portable XRF instruments operating under air (i.e., without purging or evacuation of the region between the analyzer head and the sample) are typically limited to measurement of titanium and heavier elements (Z≧22). For this reason, XRF is often used in connection with other analysis techniques that yield information regarding the concentration of lighter elements, such as carbon, nitrogen, oxygen, phosphorous and sulfur. One such technique is spark emission spectroscopy, where a spark or arc (these terms are used interchangeably herein to denote an electrical discharge) is generated between an electrode positioned near the sample surface and the sample (or an electrode in contact with the sample) to vaporize and excite atoms of the sample. The excited atoms emit light of characteristic wavelength, which is detected and analyzed to measure elemental composition.
In common laboratory and industrial practice, a sample of a test material is analyzed serially in separate XRF and spark emission spectroscopy instruments. This practice requires the sample to be transported between the instruments, either manually or via a robotic apparatus, which increases the possibility of sample contamination and extends the analysis cycle time. Furthermore, sample surfaces may need to be prepared to different specifications for XRF and spark emission spectroscopy analyses, particularly when laboratory XRF instruments are utilized, necessitating separate sample preparation tools and procedures for the two instruments.
U.S. Pat. No. 6,801,595 (“X-ray Fluorescence Combined With Laser Induced Photon Spectroscopy” to Grodzins et al.) discloses an analytical instrument that integrates an XRF device with a laser induced photon fluorescence (LIPF) spectroscopy system. An X-ray source and a laser are arranged to irradiate overlapping regions of a sample surface, such that measurement data is obtained on the same sample volume. Among the purported advantages of conducting XRF and LIPF of the same sample volume is that the XRF data may be used to normalize LIPF data so that relative results acquired by LIPF may be made absolute. Although a device architecture of this type (whereby XRF and optical emission spectroscopy data are acquired for a common sample volume) may provide certain advantages in connection with the LIPF technique, it is not well-suited for use with spark emission spectroscopy.